Method of fabricating electron discharge devices



March 31, 1959 G. A. BOOTH ET AL 2,879,583

METHOD OF FABRICATING ELECTRON DISCHARGE DEVICES Filed Dec. 13, 1955FIG. 18

FIG. 1A

FIG. 2

GEORGE A. BNOOTH ANTHONY v. DEV. KRAUSE IN V EN TORS.

THEIR ATTORNEY.

United States Patent 2,879,583 Patented Mar. 31, 1959 METHOD orFABRICATING ELECTRON DISCHARGE DEVICES Application December 13, 1955,Serial No. 552,885

Claims priority, application Great Britain December 13, 1954 2 Claims.(Cl. 29-25.l3)

and Anthony Victor de England, assignors to Cinema- London, England, aBritish com- This invention relates to improvements in the manufactureof internally coated envelopes for electron discharge devices and isespecially concerned with envelopes comprising two major sections whichare sealed together to form a single envelope and in which a continuousinternal coating is required to extend from one portion to the other ofthe envelope.

Although the present invention is described with specific relation tothe manufacture of an internally coated envelope for a cathode-ray tube,it will be appreciated by those skilled in the art that the methodaccording to the invention may have application in the manufacture ofother electron discharge devices having internal coatmgs.

It is found convenient in the manufacture of certain types ofcathode-ray tube to form the envelope in two parts, a bulb portioncontaining a member which in operation will be scanned by a cathode raybeam and a neck portion containing an electron gun for generating acathode ray beam. The scanned member and the electron gun are formed orassembled separately in their respective envelope portions and the twoportions are sealed together to form a single envelope before the tubeis evacuated. In the majority of such cathode ray tubes it is necessaryto provide a continuous conductive coating upon the inner wall of theenvelope extending from within the neck portion to within the bulbportion, and it is often advantageous that the coating be terminated atdesired distances from the extremities of the two portions.

In the repair or salvage of electron discharge devices, the samerequirements are presented. For example, when the electron gun of acathode ray tube proves defective, it is desirable to cut away the neck"section of the tube envelope and replace it entirely with a newenvelope section containing a usable gun. It is then necessary toprovide an internal coating interconnecting the two tube sections. Inboth instances a difficulty arises, since if each of the two envelopesections is provided with an appropriate internal coating and the twosections are then sealed together the coating in the vicinity of theseal is usually destroyed or damaged by the heat necessary for thesealing operation.

It is an object of the invention, therefore to provide a new andimproved method of fabricating an internallycoated envelope for anelectron discharge device where that envelope is formed by joining twoindividual envelope sections.

It is a more specific object of the invention to provide a new andimproved method of coating the internal surface of an electron dischargedevice envelope comprising two individual sections after those sectionshave been sealed to each other.

It is another object of the invention to provide a new and improvedmethod of fabricating an internally-coated electron discharge deviceenvelope which inherently avoids damage to the internal coating due toscaling operations.

The invention is thus directed to a method of fabricating aninternally-coated envelope for an electron discharge device where theenvelope initially comprises two individual sections having mating openends each provided with an internal electrically conductive coatingextending to within a predetermined distance of the mating end. Inaccordance with the invention, the method comprises the following stepsin sequence. First, the mating ends of the two envelope sections aresealed to each other to form a complete envelope having a pair of endwalls joined by a side wall. A predetermined quantity of a liquidelectrically conductive coating material is then introduced through theside wall and flowed onto the inner side wall surface of the envelope inthe region adjacent the junction between the two sections. Thereafter,the envelope is rotated about an axis extending between the end walls todistribute the coating material upon the inner walls of the envelopeadjacent the junction of the envelope sections to form a continuouscoating extending across the envelope section junction and into contactwith the previously applied coatings of the envelope sections.

The features of the invention which are believed novel.

are set forth with particularity in the appended claims. Theorganization and manner of the operation of the invention, together withfurther objects and advantages thereof, may best be understood byreference to the following description taken in conjunction with theaccompanying drawing in which:

Figure 1A shows a first envelope section for a cathoderay tube;

Figure 1B illustrates a second envelope section for a cathode-ray tubewhich may be joined to the section shown in Figure 1A to complete thetube; and

Figure 2 illustrates the method of carrying out the present invention inthe manufacture of a cathode-ray tube from the components shown inFigures 1A and 1B.

Figure 1A shows the bulb portion of a cathode-ray tube, comprising aglass envelope section 10 which is reduced to form a neck 12 of desireddiameter and is provided with an exhaust tubulation 13. The flat end 14of the bulb has been provided in known manner with a luminescent screenand the shaded portion 15 of the envelope is coated with colloidalcarbon deposited in known manner from a suspension. A portion 16 of neck12 is free from deposited carbon to avoid the deleterious action of heatupon the layer during sealing.

Figure 1B shows a tubular glass envelope section 17 provided at one endwith a press 18 through which pass leads 19 connected with aconventional electron gun 20. The shaded part 21 of envelope section 17is coated with colloidal carbon and the part 22 left free of anydeposit. The diameter of the open end 23 of the envelope section 17 isthe same as that of the neck end 12 of bulb section 10.

To complete the cathode-ray tube the two envelope sections 10, 17 aremounted coaxially in a known type of glass-working lathe (not shown)with their open ends adjacent and these ends are then sealed together byknown techniques to yield a complete but unevacuated cathode-ray tube asshown in Figure 2.

In accordance with the present invention a rubber or other appropriateflexible tube 24 is now introduced through exhaust tubulation 13 andmanipulated so that its open end 25 reaches to about the center of theuncoated area 26 of the envelope which surrounds the seal between thetwo envelope portions 10, 17. An appropriate quantity of a suspension ofcolloidal graphite is now introduced through tube 24 into the envelope,the flexible tube is removed and the envelope is rotated about its axisto distribute the coating material sufficiently evenly over the hithertouncoated area 26 of the tube envelope. The coating material should besufficient in quantity to cover the entire surface of area 26 andprovide good electrical contact with the previously-applied coatings and21; any excess material merely forms an additional layer upon coatings15 and 21. The speed of rotation is not particularly critical; it mayfor example, be of the order of 60 revolutions per minute.

When the coating material has dried sufficiently the completecathode-ray tube may be connected to a pumping system by means ofexhaust tubulation l3 and evacuated in known manner. Drying of thecoating medium may be accelerated by passing dry gas through theenvelope by means of a tube inserted similarly to tube 24, or byconnecting the exhaust tubulation to a rough vacuum line independent ofthe vacuum system used for the final exhausting process.

Thus by the use of the present invention a continuous carbon coating isobtained extending from a desired part of one of the two initiallyseparate envelope sections over the. seal between the two portions andterminating at a desired part of the other of the two sections.

Where the axial extent of a coating is not required to be accuratelycontrolled the present invention may be employed to provide the whole ofthe internal coating on at least one of the envelope sections, but itwill usually be more convenient to apply any desired coating to within ashort distance of the seal before the envelope sections are assembledtogether.

Although the coating material referred to in the specific description ofthe invention is colloidal carbon the invention is not limited to theuse of this material nor does it relate solely to the manufacture ofcathode-ray tubes as it may equally well be applied in the formation ofcontinuous layers of other materials, or in other types of electrondischarge device. For example, by the use of metallic paints other kindsof conductive layer may be applied to the envelopes of electrondischarge devices; or suspensions of other materials, for exampleluminescent powders, in appropriate binding media, may be used toprovide coatings of a desired nature in for example, tubular lampscontaining an internal coating of material excited by a gas discharge.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from theinvention in its broader aspects, and, therefore, the aim in theappended claims is to cover all such changes and modifications as fallwithin the true spirit and scope of the invention.

We claim:

l. The method of fabricating an internally-coated envelope for anelectron discharge device, said envelope initially comprising twoindividual envelope sections having mating open ends and each providedwith an internal electrically conductive coating extending to within apredetermined distance of said mating end, said method comprising thefollowing steps in sequence: sealing said mating ends of said twoenvelope sections to each other to form a complete envelope having apair of end walls joined by a side wall; introducing through said sidewall and flowing onto the inner sidewall surface of said envelope, inthe region adjacent the junction between said two sections, apredetermined quantity of a liquid electrically conductive coatingmaterial; and rotating said envelope about an axis extending betweensaid end walls to distribute said coating material upon the internalwalls of said envelope adjacent said junction of said envelope sectionsand form a continuous coating extending across the junction of saidenvelope sections into contact with the previously applied coatings ofsaid envelope sections.

2. The method of manufacturing a cathode-ray tube comprising a firstenvelope section including an exhaust tubulation and a target to bescanned by an electron beam and asecond envelope section containing anelectron gun for generating an electron beam, said two envelope sectionsinitially having mating open ends and each being provided with aninternal electrically conductive coating extending to within apredetermined distance of said mating end, said method comprising thefollowing steps in sequence: sealing said mating ends of said two envelope sections to each other to form a complete envelope having a pairof end walls joined by a side wall, said exhaust tubulation being insaid side wall; introducing through said exhaust tubulation apredetermined quantity of a liquid electrically conductive coatingmaterial and flowing said material onto the inner side wall of saidenvelope in the region adjacent the junction between said two envelopesections; and rotating said envelope about an axis extending betweensaid end walls to distribute said coating material and form a continuouscoating on the internal surface of said envelope extending across thejunction of said envelope sections and into electrical contact with thepreviously-applied coating in each of said envelope sections.

References Cited in the file of this patent UNITED STATES PATENTS2,619,430 Fink Nov. 25, 1952 2,644,770 Sadowsky July 7, 1953 2,709,414Powell et al. May 31, 1955

